Recurrent Infective Endocarditis with Mycotic Aneurysm - Imaging Modalities for the Detection of an Infective Focus.

Staphylococcus aureus bacteremia (SAB) and infective endocarditis (IE) are infections associated with considerable morbidity, requiring prompt accurate diagnosis and treatment. We present a case of a 58-year-old male patient with four episodes of recurrent symptomatic SAB treated for IE, but without positive findings on transthoracic echocardiography, transesophageal echocardiography, and fluorodeoxyglucose-positron emission tomography (FDG-PET). On the last admission, FDG-PET showed increased uptake in the right atrial appendage, and white blood cell single-photon emission computerized tomography (WBC-SPECT) was able to identify the infective focus as IE of the aortic valve. CT of the thorax also identified an associated mycotic aneurysm of the right coronary sinus. He was subsequently treated with mechanical aortic prosthesis and right coronary sinus plasty, and his symptoms did not recur till 2 years postcardiothoracic surgery. This case report demonstrates the emergence of nuclear cardiovascular imaging modalities in the diagnostic workup of IE and the utility of FDG-PET and WBC-SPECT in the identification of the infective focus. Patients with possible IE from the modified Duke criteria should be considered for FDG-PET or WBC-SPECT to enhance sensitivity. Peripheral mycotic aneurysms are a common complication of left-sided IE, which can present late into the disease process, and aortic imaging should be considered in patients with recurrent endocarditis to identify this. Copyright:

INTRODUCTION

Staphylococcus aureus bacteremia (SAB) is a serious bacterial infection with a 30% mortality rate.[1] The first step is the identification and removal of the source of infection. This is through careful history-taking and physical examination and, if required, diagnostic evaluation through additional imaging.

One imaging modality indicated is computerized tomography (CT) with contrast to identify potential foci in the form of intra-abdominal or deep soft tissue infection. Another imaging modality is echocardiography to detect possible infective endocarditis (IE). Early transthoracic echocardiogram (TTE) or transesophageal echocardiogram (TOE) is recommended under the European Society of Cardiology guidelines, as 22% of the patients with SAB have IE.[23] Echocardiographic findings are one of the major modified Duke criteria for the diagnosis of IE. TOE is more sensitive than TTE though both have diminished sensitivity in patients with prosthetic valves or devices.[24]

The emergence of new modalities for cardiovascular imaging has led to increased sensitivity in the diagnosis of IE.[2] Fluorodeoxyglucose-positron emission tomography (FDG-PET) and white blood cell single-photon emission CT (WBC-SPECT) are recommended in patients with high clinical suspicion but with negative echocardiographic findings.[256]

Here, we report a case of a patient with abnormal aortic valve morphology and recurrent SAB who was treated for recurrent IE due to a lack of disease foci on initial imaging. This case demonstrates the importance of multimodality imaging in the diagnosis and management of IE and its associated complications.

CASE PRESENTATION

A 58-year-old man presented with fever and malaise from SAB with no obvious source of infection on examination. He had a background of hypertension and type 2 diabetes mellitus. CT of the thorax, abdomen, and pelvis was not able to elucidate the source of the infection. TOE showed a thickened aortic valve with calcification of the noncoronary cusp but no overt signs of IE (no vegetations or significant valvular regurgitation). Due to a lack of an infective source, he was treated as presumed IE in view of abnormal aortic valve with 6 weeks of antibiotics, and he remained well immediately on discharge.

Two years later, he had an ST-segment elevation myocardial infarction (STEMI), for which he underwent primary percutaneous coronary intervention (PCI) with stent to distal right coronary artery. A small aneurysm at the origin of the right coronary artery was noted which was attributed to atherosclerotic disease [Figure 1]. He made an uneventful recovery and was discharged; however, 2 weeks after the STEMI, he represented with fever and chest pain. Two positive blood cultures showed SAB. TTE and TOE again showed thickened abnormal aortic valve but no evidence of IE. However, no other source of infection was identified, and he was again treated as suspected IE and discharged to finish his course of antibiotics.

Figure 1

Images from angiogram performed at the time of primary percutaneous coronary intervention showing a small well-circumscribed aneurysm at the origin of the right coronary artery

He returned a month later with rigors and joint pains. Again, positive blood cultures revealed SAB. Repeat TTE; CT of the thorax, abdomen, and pelvis; and FDG-PET were all negative. He completed 6 weeks of inpatient intravenous antibiotics and was discharged home.

Three months after, he presented with nausea, epigastric pain, and a high-grade fever. Three sets of positive blood cultures grew S. aureus (MLST clonal complex 22). WBC-SPECT of the lower chest and abdomen demonstrated a focus of low-to-moderate grade uptake at the root of the aorta, which was suspicious of IE [Figure 2].

Figure 2

White blood cell single-photon emission computerized tomography of the lower chest and abdomen. Left: No abnormal focus of uptake on planar acquisitions. Right: Single-photon emission computerized tomography/computerized tomography of the lower chest and abdomen demonstrates a focus of low-to-moderate grade uptake at the root of the aorta

Following this, CT of the thorax with contrast revealed a right coronary sinus aneurysm possibly involving the origin of the right coronary artery [Figure 3]. This was identified as a mycotic aneurysm, and urgent cardiothoracic opinion was sought. Repeat angiogram was not able to cannulate the right coronary artery selectively, but aortogram showed a large aneurysm arising close to the origin of the right coronary artery [Figure 4]. The patient underwent implantation of a tissue aortic valve and right coronary sinus repair. He made an uneventful recovery with no associated complications, and there was no recurrence of IE over 2 years of follow-up.

Figure 3

Computerized tomography of the thorax with contrast, transverse (top) and sagittal (bottom) views. Arrow demonstrates an irregular contrast-filled outpouching measuring 2.5 cm × 1.5 cm arising from the right coronary sinus and possibly involving the right coronary artery. RA = Right atrium, LA = Left atrium, RV = Right ventricle, LV = Left ventricle, Ao = Aorta, RCA = Right coronary artery, PV = Pulmonary vein, B = Bronchus, L = Liver, A = Aneurysm

Figure 4

Aortogram demonstrating aneurysm at the origin of the right coronary artery

DISCUSSION

Our patient presented with four episodes of symptomatic SAB but no foci of infection detected on the first-line imaging modalities. He was treated for IE due to high clinical suspicion and abnormal aortic valve, despite the lack of vegetations. In the event of the lack of identification of a source, an extended course of antimicrobial therapy is indicated.[1]

According to the European Society of Cardiology guidelines, FDG-PET and WBC-SPECT are indicated in possible IE according to the modified Duke criteria.[256] In our patient, FDG-PET was not able to initially identify an infective focus, but WBC-SPECT detected an area which was suspicious of aortic valve IE. Radiolabeled WBC-SPECT is more specific than FDG-PET in the detection of an infectious focus as it uses radiolabeled leukocytes that accumulate in a time-dependent fashion by comparing early images at 4 h to late images at 24–48 h, whereas PET is performed 1 h after administration of FDG.[78]

In our patient, CT of the thorax identified a mycotic aneurysm of the right coronary sinus. Mycotic aneurysms are a common complication of left-sided IE and are associated with considerable morbidity.[9] They can be found in intracranial, intra-abdominal, coronary, and peripheral limb arteries and may present late into the disease process.[9] It is difficult to ascertain at which point in the patient's presentation the mycotic aneurysm developed, though once present, it became a source of SAB itself. Retrospectively, the aneurysm observed during primary PCI was unlikely to represent atherosclerotic change as it was relatively well circumscribed and likely represents small mycotic aneurysm. Since first detection, it led to three further episodes of SAB which necessitated surgical intervention. This raises the point of suspecting mycotic aneurysm in recurrent IE as the following episodes could have been prevented with earlier intervention.

CONCLUSION

This case therefore demonstrates the importance of alternative nuclear imaging to enhance the diagnostic sensitivity of the modified Duke classification for IE and to consider mycotic aneurysm as an important source of SAB in recurrent IE.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the legal guardian has given his consent for images and other clinical information to be reported in the journal. The guardian understands that names and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.